1. Field of the Invention
This invention relates to the production of pentachloronitrobenzene.
2. Brief Description of the Prior Art
Pentachloronitrobenzene (sometimes referred to herein as PCNB) is widely used today as a soil fungicide. It is particularly useful in controlling plant diseases caused by botrytis, fusarium, rhizoctonia and anthracnose.
Several methods are known for the preparation of PCNB. For example, U.S. Pat. No. 4,026,955, which issued on May 31, 1977 to Breaux, Newman and Quinnett, teaches one such process. That patent teaches reacting pentachlorobenzene and a mixed nitration acid in three stages having specific temperature requirements. U.S. Pat. No. 4,057,590, which issued on Nov. 8, 1977 to Gay, discloses a low temperature process for making PCNB by reacting pentachlorobenzene with substantially pure nitric acid. Also, U.S. Pat. No. 4,138,438, which issued on Feb. 6, 1979 to Gay, teaches another multi-step reaction between pentachlorobenzene and a mixed nitration acid and HCl. And U.S. Pat. No. 4,147,732, which issued on Apr. 3, 1979 to Mendiratta, discloses a process with a two-stage reactant mixing step wherein pentachlorobenzene is first mixed with sulfuric acid and then concentrated nitric acid is added.
While the processes disclosed by these four references represent significant advances in producing relatively high purity PCNB, there is still a need in the art to be able to produce high purity PCNB from precursors other than pentachlorobenzene, which is not always commercially available. The present invention covers such a process for making PCNB from a precursor that was unthought of for this use until the present invention.